A conventional capacitor of this kind is described with reference to FIG. 17 and FIG. 18.
As FIG. 18 shows, a capacitor element 40 comprises a pair of electrode plates 37a and 38b, lead tabs 38a to 38d connected to the electrode plates 37a and 37b and a separator 39. The pair of electrode plates 37a and 38b, to which the lead tabs 38a to 38d are connected, are wound with the separator 39 sandwiched therebetween.
As FIG. 17 shows, the capacitor element 40 is contained in a bottomed cylindrical case 42 and fixed in position by a locating member 43 disposed on the inner bottom of the case 42. A terminal plate 44 seals an opening of the case 42 using an O ring 47. Terminals 45 for external connection are mounted on the terminal plate 44 and connected to the respective lead tabs 38a to 38d. A pressure vent 46 is provided on the terminal plate 44. The conventional capacitor is structured as described above.
In recent years, requirements from the market have been increasing for a capacitor to have a lower resistance and a smaller size. When reducing the internal resistance with the capacitor of the foregoing structure, there are the following methods:
1. increasing the number of lead tabs like the lead tabs 38a to 38d; and PA1 2. optimizing the connecting positions of lead tabs such as 38a to 38d.
In addition to the methods of increasing the number of lead tabs, the lead out resistance, or resistance of electrical current collector, of the capacitor element 40 can be reduced as the number of lead tabs is increased as Equation 1 shows. When it comes to connecting the lead tabs, which are increased in number, to the terminal 45 for external connection, the increased number of lead tabs overlaid one over another have to be connected to a lead tab connecting member of the terminal 45. However, there is a limit in the number of lead tabs that are allowed to be connected to the lead tab connecting member of the terminal 45 because of such problems as a limited available space in the case 42, workability involved with lead tab connection, reliability of connection and the like, thereby prohibiting the number of lead tabs from being increased indiscriminately. EQU Resistance of Electrical Current Collector=1/(3.times.n.sup.2).times.(3.times.(L.sub.x /L-1/2).sup.2 +1/4).times.L/W.times..rho./tp1 (Equation 1)
where n: the number of lead tabs, L.sub.x : a distance between the end of electrode and the lead tab, L: a length of electrode, W: a width of electrode, .rho.: specific resistance of aluminum and tp1: a thickness of electrode.
Regarding the optimizing the connecting positions of the lead tabs, when the distances between adjoining lead tabs of a plurality of lead tabs such as 38a to 38d that are connected to electrodes are made equal to one another and also the distances between the end parts of electrodes 37a and 37b and the lead tabs 38a and 38c, which are located closest to the end parts of respective electrodes 37a and 38b, are made 1/2 of the distances between the end parts of electrode 37a and 37b and the lead tabs 38b and 38d, respectively, the lead out resistance of the electrodes 37a and 37b of the capacitor element 40 becomes an ideal value in resistance.
However, when these electrodes are wound together, the positions of lead tabs 38a to 38d led out of the respective electrodes 37a and 37b tend to be shifted in position as the lead tabs 38a to 38d move away from the center of winding, resulting in an inadvertent problem of the lead out resistance of the electrodes 37a and 37b being increased in comparison with the foregoing ideal resistance.
With a capacitor having a structure formed by the method proposed by the same inventors of the present invention in the Japanese Patent Application No. H09-322596, when both terminals of cathode and anode electrodes are arranged to be taken out in the same direction, such problems as difficulties in reducing the height of the capacitor due to a complicated internal structure and also in producing the capacitor in large quantities have been left unsolved.
The present invention aims to address the above problems and aims at providing a capacitor that enables a reduction in internal resistance as well as in the number of components and in size.